CHEMICAL MECHANISM OF INACTIVATION OF BEE VENOM PHOSPHOLIPASE-A2 BY THE MARINE NATURAL-PRODUCTS MANOALIDE, LUFFARIELLOLIDE, AND SCALARADIAL

Inhibition of bee venom phospholipase A2 (PLA2) by manoalide (1) and luffariellolide (2) involves the initial formation of a Schiff base (imine) between a lysine residue on PLA2 and an aldehyde group on each of the drugs. Model reactions employing a primary amine in place of the lysine residue were studied by H-1 NMR spectroscopy. Amines reacted at the gamma-hydroxybutenolide ring of 2 to produce gamma-(alkylamino)butenolides 6a,b, which are cyclized forms of the corresponding Schiff bases. Manoalide methyl analogue (MMA, 12), which is a simple analogue of the reactive portion of 1, reacted similarly. The gamma-(n-butyl-amino) butenolide 6b reacted with hydroxylamine to form the oxime 8 with concomitant release of n-butylamine. When the luffariellolide-PLA2 and manoalide-PLA2 adducts were treated with hydroxylamine, the PLA2 activity was substantially recovered, but the activity was not recovered if the luffariellolide-PLA2 adduct was reduced with sodium borohydride prior to hydroxylamine treatment. PLA2 activity could be significantly recovered by treatment of the initial scalaradial 3a-PLA2 adduct with hydroxylamine but the final adduct, which is proposed to be a pyrrole (20), could not be cleaved.